This application seeks renewal funding for a unique and innovative longitudinal study of adopted and non-adopted families. The Sibling Interaction and Behavior Study (SIBS) includes 409 adopted and 208 non-adopted families. At intake, each family consisted of pair of adolescent siblings and their rearing parents, a total of 2394 individuals. SIBS offspring have completed an intake assessment in mid-adolescence, a first follow-up (FU1) assessment in late-adolescence, and are in the midst of a second follow-up (FU2) assessment in early adulthood. Rate of participation at FU1 and to date in FU2 is well above 90 percent. Intake and FU assessments are extensive and include: 1) comprehensive assessment of common externalizing (e.g., conduct disorder, substance use disorders, ADHD) and internalizing (depression, anxiety disorders) psychopathology; 2) substance use, abuse, and dependence; 3) individual-level markers of risk (personality, academic ability and progress); 4) family relationships (both parent-offspring and sibling); and 5) other environmental risk factors (e.g., peer group, religiousness, life stress, neighborhood). The current application has 4 specific aims, to: 1) complete the FU2 assessment, 2) analyze FU1 and FU2 data to determine the nature of familial risk for common mental disorders; 3) use the principle of Mendelian Randomization to test the effect of adolescent alcohol use and misuse on risk of mental health and substance use disorders in early adulthood; and 4) determine whether individuals adopted in infancy are at heightened risk for mental disorders as young adults. Analysis of SIBS intake data demonstrates that this is a unique study that is making important observations on, for example, the effect of maternal depression, the impact of parent antisocial behavior, the consequences of adolescent alcohol abuse, and the mental health of US adopted youth. Continued support for this program of research will allow us to chart the trajectory of the development of common mental disorders from mid-adolescence through early adulthood, using an adoption design that allows us to identify familial environmental as well as genetic contributions to risk.